Merge "fix(nix fmt): remove the default "." argument" into main

doc/manual/change-authors.yml

@@ -147,3 +147,6 @@ winter:
 
 yshui:
   github: yshui
+
+zimbatm:
+  github: zimbatm

doc/manual/rl-next/nix-fmt-default-argument.md

@@ -0,0 +1,38 @@
+---
+synopsis: Removing the `.` default argument passed to the `nix fmt` formatter
+issues: []
+prs: [11438]
+cls: [1902]
+category: Breaking Changes
+credits: zimbatm
+---
+
+The underlying formatter no longer receives the ". " default argument when `nix fmt` is called with no arguments.
+
+This change was necessary as the formatter wasn't able to distinguish between
+a user wanting to format the current folder with `nix fmt .` or the generic
+`nix fmt`.
+
+The default behaviour is now the responsibility of the formatter itself, and
+allows tools such as treefmt to format the whole tree instead of only the
+current directory and below.
+
+This may cause issues with some formatters: nixfmt, nixpkgs-fmt and alejandra currently format stdin when no arguments are passed.
+
+Here is a small wrapper example that will restore the previous behaviour for such a formatter:
+
+```nix
+{
+  outputs = { self, nixpkgs, systems }:
+    let
+      eachSystem = nixpkgs.lib.genAttrs (import systems) (system: nixpkgs.legacyPackages.${system});
+    in
+    {
+      formatter = eachSystem (pkgs:
+        pkgs.writeShellScriptBin "formatter" ''
+          if [[ $# = 0 ]]; set -- .; fi
+          exec "${pkgs.nixfmt-rfc-style}/bin/nixfmt "$@"
+        '');
+    };
+}
+```

src/nix/fmt.cc

@@ -39,14 +39,8 @@ struct CmdFmt : SourceExprCommand {
         Strings programArgs{app.program};
 
         // Propagate arguments from the CLI
-        if (args.empty()) {
-            // Format the current flake out of the box
-            programArgs.push_back(".");
-        } else {
-            // User wants more power, let them decide which paths to include/exclude
-            for (auto &i : args) {
-                programArgs.push_back(i);
-            }
+        for (auto &i : args) {
+            programArgs.push_back(i);
         }
 
         runProgramInStore(store, UseSearchPath::DontUse, app.program, programArgs);

tests/functional/fmt.sh

@@ -26,7 +26,10 @@ cat << EOF > flake.nix
   };
 }
 EOF
-nix fmt ./file ./folder | grep 'Formatting: ./file ./folder'
+# No arguments check
+[[ "$(nix fmt)" = "Formatting(0):" ]]
+# Argument forwarding check
+nix fmt ./file ./folder | grep 'Formatting(2): ./file ./folder'
 nix flake check
 nix flake show | grep -P "package 'formatter'"
 

tests/functional/fmt.simple.sh

@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-echo Formatting: "${@}"
+echo "Formatting(${#}):" "${@}"